Well-known slipform pavers are typically used for laying down long strips of concrete as used, for example, on highways, airport runways and the like. The pavers are continuously supplied with fresh concrete as they travel in the direction of the strip, and they form the freshly supplied concrete into a rectangular, cross-sectional shape and properly finish the top surface of the strip after which the strip of concrete is allowed to set and harden. After the concrete has hardened, expansion joints are normally sawed across the width of the strip, and to maintain the integrity of the strip, dowel bars are inserted into the fresh concrete. The dowel bars are arranged parallel to the length of the strip and typically have diameters that range from about 1 inch to 2 inches and lengths from 12 to 24 inches.
Slipform pavers capable of inserting dowel bars as the strip of concrete is being laid down are well-known and are produced and widely distributed, for example, by the assignee of this patent application.
Dowel bar inserters place a line of dowel bars across the slab being formed and simultaneously insert from about 12 to 34 or more dowel bars depending upon the width of the strip being paved. Center-to-center spacing between the dowel bars typically varies between about 12 to 18 inches. As will be further described below, the mechanism that simultaneously inserts the dowel bars must remain stationary with respect to the strip of concrete being laid down while the dowel bars are inserted. The dowel bar inserter must therefore be able to move relative to the remainder of the paver during the dowel bar insertion.
Sets of dowel bars are regularly placed at intervals of typically about every 15 feet (4.57 M) in the direction of machine travel. Slipform pavers usually operate at speeds of up to 15 feet per minute, and more at times. In order to not impede the progress of the paver, the entire dowel bar insertion process must be completed in less time, at a speed of 15 feet per minute in less than one minute, or the speed of the paver must at least intermittently be reduced.
U.S. Pat. No. 6,579,037 (the “'037 patent”) discloses a paver with a widely used dowel bar inserter, relevant portions of which are reproduced below to facilitate the reading and understanding of the present invention, and the '037 patent in its entirety is further incorporated herein by reference.
Prior art inserters of the type disclosed in the '037 patent required a manual loading of dowel bars into dowel bar holding cups, during which time the dowel bar inserter transport chains must be stopped. Such inserters reciprocably move the chains from a loading station for the dowel bars to their required insertion positions across the width of the concrete strip being laid down. This turned out to be a relatively slow process that frequently prevented paver operators from attaining the desired concrete laying machine speed of about 15 feet per minute, the machine speeds at times dropping to as low as 9 feet per minute or less.
This delay in timely completing the dowel insertion process affects the entire slipform paver because it slows down the concrete laying speed that can be attained. This is highly undesirable because it increases overall concrete laying costs.